Liquid crystal display having a pixel area divided into multiple domains

ABSTRACT

A liquid crystal display includes a first substrate having a plurality of pixel areas. At least one pair of first and second protrusions is formed at each pixel area. A pixel electrode is formed at each pixel area. The pixel electrode has an opening pattern exposing the first protrusion while covering the second protrusion. A second substrate faces the first substrate. A common electrode is formed at the second substrate. Alternatively, the opening pattern and the protrusions may be formed in parallel.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.11/107,929, filed on Apr. 18, 2005, now U.S. Pat. No. 7,110,078 which isa continuation of U.S. patent application Ser. No. 10/699,819 filed Nov.4, 2003 now U.S. Pat. No. 6,894,753, issued on May 17, 2005, which is adivisional of U.S. patent application Ser. No. 09/559,483 filed Apr. 27,2000 now U.S. Pat. No. 6,657,695, issued on Dec. 2, 2003, which claimspriority to Korean Patent Application No. 1999-26027, filed on Jun. 30,1999 and Korean Patent Application No. 1999-28449, filed on Jul. 14,1999, the disclosures of which are incorporated by reference herein intheir entirety.

BACKGROUND OF THE INVENTION

(a) Field of the Invention

The present invention relates to a liquid crystal display and, moreparticularly, to a vertical alignment liquid crystal display which has astructure capable of dividing a pixel area into multiple domains withdifferent orientation directions of liquid crystal molecules.

(b) Description of the Related Art

Generally, liquid crystal displays have a structure where a liquidcrystal is sandwiched between two substrates, and an electric field isapplied to the liquid crystal display to control the amount of lighttransmission.

In the twisted nematic (TN) liquid crystal displays, the liquid crystalmolecules injected into the gap between the two substrates are orientedparallel to the substrates, and spirally twisted with a predeterminedpitch. The long axis (usually called the “director”) of the liquidcrystal molecules continuously varies in orientation direction, and theviewing angle characteristics depend upon such orientation directions ofthe liquid crystal molecules

However, the TN liquid crystal display, light is not completely blockedat an off state in the normally black mode so that a poor contrast ratioresults. The contrast ratio is altered depending upon the viewing angle,and there is a half tone of brightness difference depending on theviewing angle so that stable picture images cannot be obtained.Furthermore, the picture qualities at side edge portions of the screenare not symmetrical to each other with respect to the middle portion.These all result in poor viewing angle characteristics.

However, the vertical alignment liquid crystal displays where the liquidcrystal molecules are vertically aligned in the absence of a voltage buttwisted in various directions with the voltage applied exhibitexcellence in various aspects, such as contrast ratio and response speedcompared to the TN liquid crystal displays. Furthermore, when acompensation film is used to divide the twisting of the liquid crystalmolecules in various predetermined directions, a wide viewing angle canbe effectively obtained.

Recently, a technique for forming an alignment control member such as apyramid-shaped protrusion on the substrates, a technique for forming anopening pattern at the transparent electrodes, and a technique forforming a protrusion pattern on one of the substrates while forming anopening pattern at the other substrate have been proposed as methods tocontrol the orientation directions of the liquid crystal molecules. Theprotrusion or opening pattern is designed to achieve four domaindivisions in the orientation direction of the liquid crystal moleculesat which the efficiency of light usage becomes highest.

FIGS. 1A and 1B are cross sectional views of a liquid crystal displayaccording to a prior art where the orientation states of liquid crystalmolecules are illustrated in the absence and presence of the voltageapplication.

As shown in the drawings, a transparent pixel electrode 11 is formed ata bottom substrate 10, and a first opening portion 1 is formed at thepixel electrode 11. A top substrate 20 facing the bottom substrate 10 isprovided with a transparent common electrode 21. A second openingportion 2 is formed at the common electrode 21. The bottom and topsubstrates 10 and 20 are arranged such that the first opening portion 1is displaced with respect to the second opening portion 2. Negativedielectric anisotropy liquid crystal molecules 30 are injected into thegap between the bottom and top substrates 10 and 20.

As shown in FIG. 1A, the liquid crystal molecules 30 are orientedperpendicular to the substrates 10 and 20 in the absence of the voltageapplication.

As shown in FIG. 1B, when voltage is applied to the pixel electrode 11and the common electrode 21, most of the regions at the pixel area areunder the influence of an electric field normal to the substrates 10 and20, but the regions adjacent to the opening portions 1 and 2 are under afringe field beginning from the edges of the opening portions 1 and 2and focused onto the common electrode 21 and the pixel electrode 11,respectively. As the negative dielectric anisotropy liquid crystalmolecules 30 are inclined to orient in a direction normal to that of theelectric field, the long axes of the liquid crystal molecules adjacentto the opening portions 1 and 2 are twisted while being tilted withrespect to the substrates 10 and 20. In this case, two side regions ofeither of the opening portions 1 and 2 where the orienting directions ofthe liquid crystal molecules 30 are opposite to each other are presentso that the optical characteristics of the two side regions arecompensated, resulting in a wide viewing angle.

FIGS. 2A and 2B are cross sectional views of a liquid crystal displayaccording to another prior art where the orientation states of liquidcrystal molecules are illustrated in the absence and presence of voltageapplication.

As shown in FIGS. 2A and 2B, a pixel electrode 12 based on a transparentconductive material such as indium tin oxide is formed at a bottomsubstrate 10, and a pyramid-shaped first protrusion 13 and a verticalalignment film (not shown) are sequentially formed on the pixelelectrode 12. A transparent common electrode 22 is formed at a topsubstrate 20, and a second pyramid-shaped protrusion 23 and a verticalalignment film (not shown) are sequentially formed at the commonelectrode 22. Negative dielectric anisotropy liquid crystal molecules 30are injected into the gap between the vertical alignment films of thebottom and top substrates 10 and 20.

As shown in FIG. 2A, in the absence of voltage application, most of theliquid crystal molecules 30 are oriented perpendicular to the verticalalignment films, but the liquid crystal molecules 30 positioned close tothe protrusions 13 and 23 are tilted with respect to the verticalalignment films at predetermined angles.

As shown in FIG. 2B, when voltage is applied to the pixel and commonelectrodes 12 and 22, the liquid crystal molecules are twisted in adirection parallel to the substrates 10 and 20. As the liquid crystalmolecules 30 positioned close to the protrusion 13 are tilted in theopposite directions with respect to the region of the protrusion 13 inthe absence of the voltage application, the twisting directions thereofare also opposite to each other with the voltage applied. Therefore, twoside regions of the protrusion 13 where the twisting directions of theliquid crystal molecules are opposite to each other are present so thatthe optical characteristics of the two regions are compensated,resulting in a wide viewing angle. In addition, disclination regionswhere the orientation directions of the liquid crystal molecules 30 aredisorderly altered are focused at the regions of the protrusions 13 and23 so that a black matrix for shielding the disclination regions can beformed in a predetermined manner.

However, in order to fabricate the above-described liquid crystaldisplays, additional processes for forming the protrusions 13 and 14 orthe opening portions 1 and 2 must be performed.

On the one hand, in the case of the liquid crystal display shown inFIGS. 1A and 1B, a wet etching process for forming the opening portion 2at the ITO-based common electrode 21 of the top substrate 20 should beprovided. Furthermore, in order to prevent the color filter from beingcontaminated or damaged due to the etching solution, a protective layerof organic or inorganic materials should be coated onto the color filterbefore the ITO processing.

On the other hand, in the case of the liquid crystal display shown inFIGS. 2A and 2B, before the formation of the protrusions 13 and 23,separate organic layers should be coated onto the pixel electrode 12 andthe common electrode 22, and etched.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a vertical alignmentliquid crystal display which has a multi-domain pixel structure.

It is another object of the present invention to provide a verticalalignment liquid crystal display with a multi-domain pixel structurewhich can be fabricated in a simplified manner.

These and other objects may be achieved by a liquid crystal display withthe following structure.

According to one aspect of the present invention, the liquid crystaldisplay includes a first substrate having a plurality of pixel areas. Atleast one pair of first and second protrusions formed parallel to eachother are provided at each pixel area. A pixel electrode is formed ateach pixel area. The pixel electrode has an opening pattern exposing thefirst protrusion while covering the second protrusion. A secondsubstrate faces the first substrate, and a common electrode is formed atthe second substrate. A negative dielectric anisotropy liquid crystal issandwiched between the first and second substrates. A first verticalalignment film is coated on the common electrode, and a second verticalalignment film is coated on the pixel electrode and the firstprotrusion.

A thin film transistor is formed at each pixel area. The thin filmtransistor includes a gate electrode, a gate insulating layer formed onthe gate electrode, a semiconductor pattern formed on the gateinsulating layer over the gate electrode, and source and drainelectrodes overlapped with side edges of the semiconductor pattern. Aprotective layer covers the thin film transistor.

The first and second protrusions are formed with the same material as atleast one of the gate insulating layer, the semiconductor pattern andthe protective layer. The pixel electrode and the common electrode areformed with indium tin oxide or indium zinc oxide.

According to another aspect of the present invention, the liquid crystaldisplay includes a first substrate having a plurality of pixel areas,and a plurality of protrusions formed at each pixel area of the firstsubstrate. A pixel electrode covers the protrusions. The pixel electrodehas opening portions. The opening portions and the protrusions areformed in parallel. A second substrate faces the first substrate, and acommon electrode is formed at the second substrate. A negativedielectric anisotropy liquid crystal is sandwiched between the first andsecond substrates. Vertical alignment films are coated on the commonelectrode and the pixel electrode, respectively. The cross section ofthe protrusion is shaped as a rectangle.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention, and many of the attendantadvantages thereof, will be readily apparent as the same becomes betterunderstood by reference to the following detailed description whenconsidered in conjunction with the accompanying drawings in which likereference symbols indicate the same or similar components, wherein:

FIGS. 1A and 1B are cross sectional views of a liquid crystal displayaccording to a prior art, illustrating the orientation states of liquidcrystal molecules when voltage application is absent and present,respectively;

FIGS. 2A and 2B are cross sectional views of a liquid crystal displayaccording to another prior art, illustrating the orientation states ofliquid crystal molecules when voltage application is absent and present,respectively

FIG. 3 is a cross sectional view of a liquid crystal display accordingto a preferred embodiment of the present invention, illustrating theorientation states of liquid crystal molecules when voltage applicationis absent;

FIG. 4 is a cross sectional view of the liquid crystal display shown inFIG. 3, illustrating the orientation states of the electric fields andliquid crystal molecules with the voltage applied;

FIG. 5 is a cross sectional view of the liquid crystal display shown inFIG. 3, illustrating the shapes of the electric fields at differentdomains;

FIG. 6 is a cross sectional view of the liquid crystal display shown inFIG. 3, illustrating the orientation states of the liquid crystalmolecules due to the electric fields;

FIG. 7 is a plan view of the liquid crystal display shown in FIG. 5;

FIG. 8 is a sectional view of the liquid crystal display taken along theVIII-VIII′ line of FIG. 7;

FIGS. 9A to 9C are cross sectional views of the liquid crystal displayshown in FIG. 5, illustrating the steps of processing a color filtersubstrate for the liquid crystal display in a sequential manner; and

FIGS. 10A to 10F are cross sectional views of the liquid crystal displayshown in FIG. 5, illustrating the steps of processing a TFT arraysubstrate for the liquid crystal display in a sequential manner.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of this invention will be explained with referenceto the accompanying drawings.

FIG. 3 is a cross sectional view of a liquid crystal display with a TFTarray substrate and a color filter substrate according to a preferredembodiment of the present invention.

The TFT array substrate 10 has a plurality of pixel areas at which agate electrode, a gate insulating layer, a semiconductor pattern, andsource and drain electrodes are sequentially formed. As shown in FIG. 3,a pair of pyramid-shaped protrusions 11 and 12 are formed at each pixelarea. The protrusions 11 and 12 may be formed with the same material asthe semiconductor pattern, the gate insulating layer, or a protectivelayer covering the source and drain electrodes.

A pixel electrode 13 covers the protrusion 12 and the TFT arraysubstrate 10, and it has an opening pattern 5 exposing the protrusion11. A first vertical alignment film 14 is coated on the pixel electrode13 and the exposed protrusion 11 to vertically align negative dielectricanisotropy liquid crystal molecules 31 and 32.

In addition, the color filter substrate 20 is sequentially overlaid witha transparent common electrode 21 and a second vertical alignment film22 such that they face the TFT array substrate 10.

The liquid crystal molecules 31 and 32 are injected into the gap betweenthe TFT array substrate 10 and the color filter substrate 20. Most ofthe liquid crystal molecules 31 are oriented perpendicularly to thesubstrates 10 and 20 due to the vertical alignment films 21 and 22,whereas the liquid crystal molecules 32 adjacent to the protrusions 11and 12 are tilted with respect to the substrates 10 and 20, atpredetermined angles.

FIG. 4 illustrates the orientation states of the liquid crystalmolecules under the application of voltage.

As shown in FIG. 4, when voltage is applied to the pixel electrode 13 ofthe TFT array substrate 10 and the common electrode 21 of the colorfilter substrate 20, a vertical electric field is formed at most of thepixel area, excepting some regions. That is, a hill-shaped electricfield E1 is formed at the pixel regions at either side of the openingpattern 5 of the pixel electrode 13 exposing the protrusion 11. Thehill-shaped electric field E1 begins from the boundary of the openingpattern 5 and is focused onto the common electrode 21 of the colorfilter substrate 20. Furthermore, a valley-shaped electric field E2 isformed at the side pixel regions of the protrusion 12 covered by thepixel electrode 13. The valley-shaped electric field E2 begins from thecenter of the protrusion 12, and spreads over the common electrode 21.

The electric fields E1 and E2 are symmetrically formed with respect toeach center of the opening pattern 5 and the protrusion 12, making theliquid crystal molecules 33 at the side regions thereof to be tilted inopposite directions. In this way, the optical characteristics of theliquid crystal molecules 33 at the side pixel regions related to theopening pattern 5 or the protrusion 12 are compensated, resulting inwide viewing angle.

Disclination areas D1 and D2 where liquid crystal molecules 34 aredisorderly oriented are present at the borderline pixel regions betweenthe side pixel regions. Such disclination areas appear to be wider atthe borderline pixel region related to the opening pattern 5 than at theborderline pixel region related to the second protrusion 12. However,since the first protrusion 11 is internally formed at the openingpattern 5, the width of the disclination area D1 related to the openingpattern 5 is significantly reduced. The reason is that the orientationdirection of the liquid crystal molecules 32 at the opening pattern 5before the application of voltage stands in the direction of theelectric field E1 with a relatively large angle. As the liquid crystalmolecules 32 are initially tilted at a predetermined angle with respectto the substrate 10, the required energy for vertically aligning theliquid crystal molecules 32 with respect to the direction of theelectric field E1 is relatively low so that the orientation of most ofthe liquid crystal molecules 33 can be easily established. Therefore,the relatively wide disclination area related to the opening pattern 5alone can be narrowed with the addition of the protrusion 11, andfocused onto the apex of the protrusion 11 in a stable manner.

FIG. 5 is a cross sectional view of a liquid crystal display accordingto a second preferred embodiment of the present invention, whereelectric fields for realizing multi-domain orientation of liquid crystalmolecules are illustrated.

As shown in FIG. 5, a protrusion pattern 15 having a rectangular-shapedcross section is formed at the gate insulating layer and the protectivelayer over the TFT array substrate 10, and a pixel electrode 16 ofindium tin oxide (ITO) or indium zinc oxide (IZO) covers the protrusionpattern 15. An opening pattern 3 is formed at the pixel electrode 16while being alternately arranged with the protrusion patterns 15. Atleast one protrusion pattern 15 and one opening pattern 30 are providedwithin each pixel area. The color filter substrate 20 is overlaid withcolor filters (not shown) and a transparent common electrode 25 coveringthe color filters such that they face the TFT array substrate.

When voltage is applied to the common electrode 25 and the pixelelectrode 16, electric fields E and equi-potential lines Eeq are formedbetween the TFT array substrate 10 and the color filter substrate 20.That is, a hill-shaped electric field E is formed at the opening pattern3 while beginning from the edge of the opening pattern 3 and focusingonto the common electrode 25 of the color filter substrate 20. Avalley-shaped electric field E is formed at the protrusion pattern 15while beginning from the center of the protrusion pattern 15 andspreading over the common electrode 25. Therefore, the electric fields Eand the equipotential lines Eeq uniformly appear in a symmetrical mannerwith respect to the center of the protrusion pattern 15 or the openingpattern 3.

FIG. 6 illustrates the orientation state of the liquid crystal moleculesunder the influence of the electric fields shown in FIG. 5.

As shown in FIG. 6, the negative dielectric anisotropy liquid crystalmolecules 30 injected into the gap between the two substrates 10 and 20are tilted symmetrical to each other at two side regions of either ofthe protrusion pattern 15 and the opening pattern 3 because the longaxis thereof is inclined to be oriented perpendicular to the electricfields E or parallel to the equipotential lines. Therefore, the opticalcharacteristics of the liquid crystal molecules at the two side regionsare compensated, resulting in a wide viewing angle.

FIG. 7 is a plan view of the liquid crystal display shown in FIG. 6, andFIG. 8 is a sectional view of the liquid crystal display taken along theVIII-VIII′ line of FIG. 7.

As shown in the drawings, the TFT array substrate 10 is overlaid with agate line assembly including gate lines 101 formed in the horizontaldirection, and gate electrodes 102 extended from the gate lines 101. Afirst gate insulating pattern 201 covers the gate line 101 and the gateelectrode 102. An amorphous silicon semiconductor pattern 301 is formedon the first gate insulating pattern 201 over the gate electrode 102. Adoped amorphous silicon ohmic contact pattern 402 is formed on thesemiconductor pattern 301 while being absent over the gate electrode102. Data lines 501 proceeding in the vertical direction are formed onthe first gate insulating pattern 201 such that they cross the gatelines 101. Source electrodes 502 are extended from the data lines 501while contacting the ohmic contact pattern 402 at one side, and drainelectrodes 503 are separately positioned opposite to the sourceelectrodes 502 with respect to the gate electrodes 102 while contactingthe ohmic contact pattern 402 at the other side. A first protectivepattern 601 covers the first gate insulating pattern 201, thesemiconductor pattern 301, the data lines 501, and source and drainelectrodes 502 and 503 over the gate line 101 and the gate electrode102. The first protective pattern 601 has substantially the same shapeas the first gate insulating pattern 201 except that it is removed overthe drain electrode 503. The first protective pattern 601 and the firstgate insulating pattern 201 are absent over the pixel area defined bythe neighboring gate and data lines 101 and 501.

Meanwhile, a protrusion pattern 15 having one or more protrusions isformed at the pixel area. The protrusion pattern 15 has a double layeredstructure where a second protective pattern 602 is formed on a secondgate insulating pattern 202. The second gate insulating pattern isformed with the same material as the first gate insulating pattern 201,and the second protective pattern 602 is formed with the same materialas the first protective pattern 601. The protrusion pattern 15 has aprotrusion width of 3-8 μm.

In the following preferred embodiments, the pixel area will beconsidered to have a substantially rectangular shape with first andsecond long sides, and first and second short sides. It is furtherassumed that the rectangular-shaped pixel area has an upper region withthe first short side, and a lower region with the second short side, andthe upper and lower regions are bisected by a center line.

The protrusion pattern 15 is symmetrically formed at the upper and lowerpixel regions while proceeding at 45° with respect to the center line.The protrusion pattern 15 includes top, middle and bottom protrusions.

The middle protrusion has a V-shaped base positioned around the centerline while facing the first long side of the pixel area. The V-shapedbase has a bent portion on the center line, and two wings symmetricallyextended from the bent portion up and downward while being tilted at 45°with respect to the center line. A first limb 151 is horizontallyextended from the bent portion of the V-shaped base toward the secondlong side of the pixel area along the center line, and second limbsvertically extended from the wings of the V-shaped base up and downwardalong the first long side of the pixel area, respectively.

The top protrusion of the protrusion pattern 15 has a first linear baseproceeding parallel to the upper wing of the V-shaped base of the middleprotrusion. A first limb 151 is horizontally extended from the top endof the first linear base along the first short side of the pixel area,and a second limb 152 is vertically extended from the bottom end of thefirst linear base along the second long side of the pixel area.

The bottom protrusion has a second linear base proceeding parallel tothe lower wing of the V-shaped base of the middle protrusion. A firstlimb 151 is horizontally extended from the bottom end of the secondlinear base along the second short side of the pixel area, and a secondlimb 152 is vertically extended from the top end of the linear basealong the second long side of the pixel area.

Meanwhile, a pixel electrode 16 of ITO or IZO covers the protrusionpattern 15 while contacting the exposed portion of the drain electrode50. Some portion of the pixel electrode 16 at the pixel area is removedto thereby form an opening pattern 3. The opening pattern 3 issymmetrically formed at the upper and lower pixel regions whileproceeding at 45° with respect to the center line. The opening pattern 3has top, middle and bottom opening portions.

The top opening portion is placed between the bases of the top andmiddle protrusions of the protrusion pattern 15 while proceedingparallel thereto. The bottom opening portion is placed between the basesof the middle and bottom protrusions of the protrusion pattern 15 whileproceeding parallel thereto. The middle opening portion proceeds fromthe first long side of the pixel area toward the bent portion of theV-shaped base of the middle protrusion along the center line.

Roughly, the protrusion pattern 15 and the opening pattern 3 arealternately arranged parallel to each other.

A vertical alignment film (not shown) is formed on the pixel electrode16.

The color filter substrate 20 facing the TFT array substrate 10 has alight interception layer 700 corresponding to the TFT and the gate anddata lines 101 and 501 external to the pixel area, and color filters 801and 802 corresponding to the pixel area. A common electrode 25 of ITO orIZO is formed on the color filters 801 and 802, and a vertical alignmentfilm (not shown) is coated onto the common electrode 25.

In the liquid crystal display structured with the aforementionedprotrusion pattern 15 and the opening pattern 3, the orientationdirections of the liquid crystal molecules are differentiated at the twoside regions of the protrusion pattern 15 or the opening pattern 3. Thatis, the pixel area is divided into two domains on the basis of theprotrusion pattern 15 and the opening pattern 3, respectively.Furthermore, as the portions of the opening and protrusion patterns 3and 15 at the upper region of the pixel area proceed symmetrical tothose at the lower region, the orientation directions of the liquidcrystal molecules at the upper region are also symmetrical to those ofthe liquid crystal molecules at the lower region. Consequently, thepixel area is divided into four domains where the orientation directionsof the liquid crystal molecules are differentiated, and this results ina wide viewing angle.

The protrusion pattern 15 and the opening pattern 3 are not limited tothe above shapes, but can be altered in various manners on the conditionthat the pixel area is divided into four domains based on theorientation directions of the liquid crystal molecules.

As described above, the electric field at the region of the protrusionpattern 15 is relatively wide, whereas the electric field at the regionof the opening pattern 3 is relatively narrow because it is focused onthe common electrode 25. Therefore, the pixel area can be effectivelydivided into multiple domains while improving the viewing anglecharacteristics. Furthermore, as the formation of the opening orprotrusion pattern is necessary only on the TFT array substrate side,the performance characteristics of the common electrode 25 of the colorfilter substrate are not deteriorated, and production efficiency can beenhanced.

FIGS. 9A to 9C illustrate the steps of processing the color filtersubstrate for the liquid crystal display shown in FIG. 5.

As shown in FIGS. 9A to 9C, a matrix type light interception layer 700is formed on the color filter substrate 20 to shield the periphery ofthe pixel area, and color filters 801 and 802 are formed at the pixelarea where the light interception layer is absent. Thereafter, an ITO orIZO film is deposited onto the substrate 20 to form a common electrode25. A vertical alignment film (not shown) is coated onto the commonelectrode 20 to thereby complete the color filter substrate.

FIGS. 10A to 10F illustrate the steps of processing the TFT arraysubstrate for the liquid crystal display shown in FIG. 5.

As shown in FIG. 10A, a gate line assembly including gate lines 101 andgate electrodes 102 is formed on the substrate 10, and a gate insulatinglayer 200 is then formed on the gate line assembly.

Thereafter, as shown in FIG. 10B, an amorphous silicon semiconductorlayer and a doped amorphous silicon ohmic contact layer are sequentiallydeposited onto the substrate 10, and etched together to thereby form anohmic contact pattern 401 and a semiconductor pattern 301.

As shown in FIG. 10C, a data line assembly including data lines 501, andsource and drain electrodes 502 and 503 are formed on the structuredsubstrate 10, and the ohmic contact pattern 401 is etched by using thesource and drain electrodes 502 and 503 as a mask.

As shown in FIG. 10D, a protective layer 600 is deposited onto thestructured substrate 10.

Thereafter, as shown in FIG. 10E, the protective layer 600 and theunderlying gate insulating layer 200 are etched to thereby form a firstprotective pattern 601 and a gate insulating pattern 201 over the TFT,the gate lines 101 and the data lines 601 external to the pixel area,and a protrusion pattern 15 at the pixel area. The protrusion pattern 15is formed with the second protective pattern 602 and the second gateinsulating pattern 202. Furthermore, in this step, the protective layer600 over the drain electrode 503 is removed to partially expose thedrain electrode 503 to the outside.

The layered structure of the protrusion pattern 15 may be altered byapplying different formation techniques. For instance, in the case whenthe TFT array substrate is fabricated through four mask processes, thegate insulating layer, the ohmic contact layer, the semiconductor layerand the metal layer for the data line assembly are etched together tothereby form a data line, a semiconductor pattern and an ohmic contactpattern. In this step, the protrusion pattern may be formed with themetal layer for the data line assembly, the semiconductor layer and theohmic contact layer.

As shown in FIG. 10F, a transparent conductive layer of ITO or IZO isdeposited onto the substrate 10, and etched to thereby form a pixelelectrode 16 at each pixel area, and an opening pattern 3. The pixelelectrode 16 contacts the exposed portion of the drain electrode 503,and the opening pattern 3 is positioned within the pixel electrode 16 atthe pixel area.

A vertical alignment film (not shown) is coated onto the pixel electrode16 with the opening pattern 3 to thereby complete a TFT array substrate.

The TFT array substrate is then aligned with the color filter substratesuch that the pixel electrode 16 of the former faces the commonelectrode 25 of the latter. The substrates are then combined with eachother under the application of sealant, and polarizer films areexternally attached to the substrates to thereby complete a liquidcrystal display.

In the aforementioned process, as only the TFT array substrate isstructured to have the protrusion pattern 15 and the opening pattern 3,the possible misalignment occurring when such patterns are separatelyformed at the TFT array and the color filter substrates is prevented.

Furthermore, as the protrusion pattern 15 and the opening pattern 3 ofthe TFT array substrate are formed during the step of exposing the drainelectrode 503 by etching the protective layer 600 and the gateinsulating layer 200 and the step of etching the pixel electrode 16,additional processing steps for forming the protrusion pattern 15 andthe opening pattern 3 are not required.

In addition, since the common electrode 25 of the color filter substratedoes not have any opening pattern, the photolithography process forforming such an opening pattern at the common electrode 25 or theprocess for forming an overcoat buffer layer for protecting the colorfilter from the etching solution is not required. In this way, theprocessing steps can be simplified, and the possible increase in theresistance, overetching or undercut of the common electrode 25 in thepresence of an opening pattern can be completely prevented.

The above-described structure of the liquid crystal display may bereferred to as the “enhanced vertical alignment (EV) mode.”

In the EV mode liquid crystal display, the TFT array substrate basicallyhas at least two protrusions and a pixel electrode with an openingpattern at each pixel area where one of the protrusions is covered bythe pixel electrode and the other protrusion is exposed through theopening pattern. In this structure, the orientation directions of theliquid crystal molecules can be effectively differentiated based on theprotrusion and opening patterns, and disclination regions can be reducedin width. Furthermore, as the protrusion pattern can be formed duringthe TFT formation process by using the TFT formation layers such as theprotective layer, the gate insulating layer and the semiconductor layer,and the opening pattern can be formed during the pixel electrodeformation process, separate processing steps with additional materialsfor the pattern formation are not required.

As described above, a new pattern structure capable of effectivelydividing the pixel area into multiple domains is formed at one substrateso that the processing steps can be simplified, and possiblenon-uniformity in the orientation directions of the liquid crystalmolecules at the separate domains due to misalignment of the substratescan be prevented.

While the present invention has been described in detail with referenceto the preferred embodiments, those skilled in the art will appreciatethat various modifications and substitutions can be made thereto withoutdeparting from the spirit and scope of the present invention as setforth in the appended claims.

1. A liquid crystal display, comprising: a first substrate; a gate lineassembly formed on the first substrate, the gate line assemblycomprising a gate line and a gate electrode; a gate insulating layercovering the gate line assembly; a semiconductor pattern formed on thegate insulating layer over the gate electrode; a data line assemblyformed on the gate insulating layer and the semiconductor pattern, thedata line assembly comprising a source electrode, a drain electrode anda data line, the data line crossing the gate line; a protective layercovering the gate insulating layer, the semiconductor pattern, the dataline, the source electrode and the drain electrode over the gate lineand the gate electrode except a portion of the drain electrode; aprotrusion formed at the first substrate, the protrusion comprising anunder-layer formed with the same material as the gate insulating layer,and an over-layer formed with the same material as the protective layer;a pixel electrode connected to the drain electrode and covering theprotrusion; a second substrate facing the first substrate; and a commonelectrode formed at the second substrate.
 2. The liquid crystal displayof claim 1, wherein the protective layer is an organic layer.
 3. Theliquid crystal display of claim 2, further comprising an opening, theprotrusion and the opening dividing a pixel area into a plurality ofdomains.
 4. The liquid crystal display of claim 3, wherein theprotrusion has a portion substantially parallel to a portion of theopening.
 5. The liquid crystal display of claim 2, wherein the gateinsulating layer has the same shape as the protective pattern except aportion under the drain electrode.
 6. The liquid crystal display ofclaim 2, further comprising color filters formed at the second substratecorresponding to pixel areas of the first substrate, the color filterspositioned between the common electrode and the second substrate; and alight interception layer interposed between neighboring color filters.7. The liquid crystal display of claim 2, further comprising a negativedielectric anisotropy liquid crystal sandwiched between the first andsecond substrates.
 8. The liquid crystal display of claim 2, furthercomprising vertical alignment films formed on the pixel electrode andthe common electrode to vertically align liquid crystal molecules. 9.The liquid crystal display of claim 2, wherein the common electrode isformed with indium tin oxide or indium zinc oxide.
 10. The liquidcrystal display of claim 9, wherein the pixel electrode is formed withindium tin oxide or indium zinc oxide.
 11. The liquid crystal display ofclaim 2, further comprising an ohmic contact layer disposed between thesemiconductor pattern and the source and drain electrodes.
 12. Theliquid crystal display of claim 1, wherein the protective layer isabsent at a portion of a pixel area defined by neighboring gate and datalines.